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Harcourt / Oral

Biology of extinction and persistence in apes compared to monkeys.

A. H. Harcourt, Dept. Anthropology, University of California, One Shields Ave., Davis, CA 95616, USA

     We often know the course that evolution took. For instance, apes declines at the end of the Miocene. We far more rarely know why evolution took the course that it did. Why did Australopithecus disappear, but Homo persist? To answer this sort of question for primates, and thus to increase our understanding of the process of their evolution, I compare the biology of extant primate species that persist in the face of change or destruction of their habitat with the biology of species that apparently succumb to the changes, highlighting comparisons within the apes, and between apes and monkeys. I use two measures of habitat change. One is short-term change on a local scale, namely partial conversion of primary forest to secondary forest by, e.g., selective logging. The other is long-term, regional disappearance of habitat, namely the insularization of the Asian Sunda Shelf in the Holocene. The first measures extinction and persistence on the scale of a few decades at most and a few tens of square kilometers, the latter on the scale of thousands of years and thousands of square kilometers. Data are available for eight pairs of congeners, or near-congeners in the first comparison, one member of which persisted, the other of which declined; in the second comparison, eight genera are compared, with controls for phylogenetic relationships. The results indicate that large year range, and a geographical distribution close to the equator correlate significantly with susceptibility to short-term, local change of habitat. Large body mass and low average population density are additional correlates at the long-term, regional scale of disappearance of habitat. The overall results apply in part to comparisons within the African apes, and in large part to the ape (susceptible) - monkey contrast. Specialized diet and low reproductive rate have been previously suggested as traits that might explain the decline of the apes by comparison to monkeys. This study adds some other traits for consideration. Of course, the results should also be of relevance to predicting extinction in the future, and hence to conservation.